Device and procedure for axial thrust compensation

ABSTRACT

Compensation for the axial thrust in a pump, in particular a vertical pump, having at least one drive unit and at least one rotary pump unit. In operation of the pump a compensating piston which is axially non-displaceably connected to the shaft of the impeller wheel of the rotary pump unit is subjected to a pressure difference which results from the pump pressure and a lower pressure and from which there is produced a force which is directed in opposite relationship to the axial thrust and which acts on the shaft of the impeller wheel. There are further proposed a method of axial thrust compensation and a method of retrofitting an arrangement for axial thrust compensation to a pump, in particular a vertical pump, and a retrofit module therefore.

FIELD OF THE INVENTION

The invention generally concerns a pump, in particular a vertical pump, a procedure for or method of compensating for the axial thrust which occurs in operation in a pump, and a method of retrofitting axial thrust compensation to a pump and a corresponding retrofit module for axial thrust compensation on a pump.

BACKGROUND OF THE INVENTION

The pumps being considered here have at least one impeller wheel which is driven by way of a shaft by at least one drive unit, wherein in operation an axial thrust corresponding to the pump pressure acts on the shaft of the impeller wheel. The term vertical pump is used here to denote a pump in which in use the pump shaft is oriented substantially vertically.

As mentioned hereinbefore, a force acting in the axial direction, referred to as axial thrust, acts on the shaft of the pump in operation thereof. That force results from the loading of the pump impeller wheel or wheels by the fluid to be delivered and is in opposite relationship to the delivery direction of the pump. Particularly in the case of the above-mentioned vertical pumps, that axial force causes at the pump shaft a markedly increased loading on the thrust bearings which have to carry that force. In the case of vertical pumps of the kind set forth in the opening part of this specification, the axial thrust also acts on the shaft of the drive unit. Due to the loading on the thrust bearings the axial thrust increases the wear thereof and thus shortens the service life of the bearings. The efficiency of the pump is also adversely affected. Axial thrust compensating arrangements are provided in modern high-output pumps in order to counteract that.

An example of an arrangement for compensating for the thrust in multi-stage rotary pumps is described in the published specification of DE 1 280 055. Mounted on the pump shaft is a compensating piston. Disposed on its side remote from the impeller wheel is a load-relief chamber communicating with a load-relief water return conduit so that there is a pressure difference. Disposed in the load-relief water return conduit is a regulating member, the drive of which is connected to an axial force or thrust measuring device for detecting the thrust loading on the thrust bearing. Switching devices control the regulating device in such a way that the axial load is limited to a given value, by the set pressure difference.

Patent specification DD 231829 describes a method of axial thrust compensation in rotary pumps, in which there is also a compensating piston at which a pressure difference is generated by the pump pressure and a lower pressure which is supplied by way of a load-relief water return conduit. A rotary speed measuring device and pressure measuring means arranged upstream and downstream of the compensating piston respectively pass the measured data to a computer which determines the resulting axial thrust in corresponding relationship with the rotary speed. When a difference occurs between the axial thrust and the compensating force a valve disposed in the load-relief water return conduit is actuated in such a way that a load-relief pressure is produced, at which the difference disappears.

The aforementioned method and the arrangement suffer from disadvantages. Thus, additional devices such as a valve and a drive for same or various force and rotary speed measuring devices as well as a computer unit are required to match the pump pressure and the load-relief pressure to each other. That signifies a considerable increase in the complication and expenditure in terms of manufacture and operation. Furthermore each additional device also always represents a possible source of defect and failure, which gives rise to additional costs due to repair and maintenance.

The aim of the present invention is to overcome those disadvantages.

SUMMARY OF THE INVENTION

Therefore the object of the invention is to provide a pump on which the axial thrust which occurs in operation is compensated or reduced with the lowest possible level of technical complication and expenditure.

A further object of the invention can be that of providing a method of axial thrust compensation on pumps.

Still a further object of the invention can be that of providing a method of retrofitting axial thrust compensation to an existing pump, in particular a vertical pump, so that already existing pumps can also use axial thrust compensation or a method of axial thrust compensation is employed. In this connection a further object can be that of providing a retrofit module for a self-regulated axial thrust compensation action on a pump.

To attain at least one of the above-specified objects a pump comprises at least one rotary pump unit having at least one impeller wheel drivable by at least one drive unit, wherein an axial thrust occurring in operation of the pump acts on the shaft of the impeller wheel. There is further provided a compensating piston which at least partially supports the axial thrust in self-regulating relationship and which is connected to the shaft in force-locking relationship in the axial direction of the shaft. The feed of the pump pressure or the predetermined lower pressure to the compensating piston is implemented by way of an axial passage in the shaft as a compensating conduit.

The core concept of the way in which the object is attained lies in the provision of a compensating arrangement for the axial thrust which in operation acts on the shaft of the pump, wherein there is provided a compensating piston connected to the shaft in force-locking relationship in the axial direction of the shaft and guided in a compensating cylinder for producing a compensating force which is self-regulatingly dependent on the axial thrust of the piston and which acts in opposite relationship thereto at the shaft of the drive unit. In that case the self-regulating compensating force is produced from a differential pressure between the pump pressure occurring in operation of the pump and any lower pressure than the pump pressure.

In an embodiment to reduce the loading on the thrust bearings a compensating piston which at least partially supports the axial thrust is connected to the shaft in force-locking relationship in the axial direction of the shaft. That permits the pump/drive unit to be of a very compact structure, in which, in operation of the pump, the compensating force which counteracts the axial thrust is transmitted directly and without loss to the shaft of the drive unit.

The compensating piston can be mounted essentially at any desired location of the shaft. If it is mounted between the pump unit and the drive unit that permits a very compact structure, in particular in respect of a vertical pump, to be achieved. In addition that permits a particularly advantageous feed of the respective pressure to the corresponding side of the piston.

In particular the function of the compensating piston can be self-regulating, whereby in comparison with solutions in the state of the art it is possible to dispense with additional measuring and regulating devices. That affords a considerable reduction in manufacturing complication and cost.

The thrust bearing which is less heavily loaded thereby can be smaller in size and of a simpler design, which also leads to a reduction in manufacturing complication and expenditure and minimizes costs. In addition the service life and operational reliability of the thrust bearings are increased.

In order to achieve a desired load relief effect for the thrust bearings, it may be advantageous if the assembly comprising the compensating piston and the compensating cylinder, in particular the effective piston area, is adapted to the nominal output of the drive unit. In that respect for example the size of the piston area can be so selected upon production that, at the maximum pump output or the nominal output, the load-relief force generated is so great that the axial thrust produced is very largely compensated. If matching is implemented in relation to the maximum output, a reversal of the axial thrust is also reliably prevented, for example in the event of a piston area which is excessively large.

In order to keep separate from each other the media which are under different pressures at the top side and the underside of the compensating piston and in order to permit the creation of a pressure difference at the piston, in an embodiment the compensating piston can be guided in a cylinder.

As the compensating piston which is fixedly connected to the shaft must be displaceable relative to the cylinder, a given embodiment provides that the cylinder is fixed to the side of the motor, that faces towards the pump. The compact structure is thereby additionally promoted. In addition in that way the complication and expenditure in respect of construction, assembly and maintenance is minimized as for example there is already a fixing plane on the drive unit and does not first have to be created or formed, in contrast to the pump side.

In an alternative configuration the assembly of the compensating piston and the compensating cylinder is provided upstream of the rotary pump unit in the delivery direction. With such an assembly, the compensating piston and the compensating cylinder can act as a hydraulic additional bearing which contributes to a considerable relief of load on the main thrust bearing, whereby the latter in turn can be of a significantly smaller and simpler structure. The hydraulic additional bearing runs almost wear-free and has a markedly lower level of frictional resistance than conventional thrust bearings.

In the aforementioned embodiment, it is advantageous to use the suction pressure of the rotary pump unit as the lower pressure as a direct fluidic communication from the suction side of the rotary pump unit to the corresponding side of the compensating piston, namely the piston side that faces towards the rotary pump unit, can be very easily made. It will be appreciated that it is alternatively possible for the ambient pressure or any other predetermined lower pressure to be supplied as the pump pressure by way of a corresponding compensating conduit.

In the structure in which the suction pressure of the pump is used as the desired lower pressure, automatic adaptation of the axial thrust and the compensating thrust takes place, when the pump output changes.

If the ambient pressure is used as the lower pressure, retrofitting of the arrangement according to the invention to conventional vertical pumps is possible without structural changes to the pump.

It may be advantageous to provide a direct fluidic communication with the pressure side of the pump, for the side of the compensating piston at which the higher pressure is to occur. The pump pressure can act directly and without loss on the compensating piston in such a structurally simple design configuration.

In order to be able to counteract the axial thrust the lower pressure must be fed to the side of the compensating piston, which faces in the direction of the load-relief force produced. In a structurally simple design, that can be achieved by way of a compensating conduit which can be easily adapted to the prevailing aspects of existing drive and/or pump units.

In order to avoid the fitment of additional components such as conduits and fixing elements, in an advantageous development the compensating conduit can be in the form of an axial passage, for example in the form of an axial bore, in the shaft of the drive unit and/or the rotary pump unit.

It will be assumed hereinafter that, in a vertical pump, the drive unit is arranged above the rotary pump unit. In that case the ambient pressure can be passed by way of an axial passage such as for example an axial bore as a compensating conduit in the shaft passing through the drive unit, to the corresponding side of the compensating piston. In the situation where the suction pressure is used or is to be used as the predetermined lower pressure, the suction pressure can be passed through a corresponding axial passage, for example in the form of an axial bore, as the compensating conduit through the shaft passing through the rotary pump unit, to the corresponding side of the compensating piston. In that respect in principle the vertical pump can have a single shaft, that is to say a shaft which is made in one piece, as the drive shaft and the pump shaft, but designs are also possible which have a divided shaft arrangement, that is to say with a multi-part shaft. A divided shaft is generally involved or is of advantage in particular if the individual functional units such as for example motor units or pump units are of a modular structure and thus the pump is scalable. Finally it should also be noted that the drive unit can also be disposed under the rotary pump unit, in which case then the foregoing description is correspondingly modified.

As a further advantageous configuration, the assembly consisting of the compensating piston and the cylinder (compensating piston/cylinder arrangement) can be in the form of a retrofit module. Such a retrofit module can be equipped for example with suitable flanges so that it can be easily fixed between the drive unit and the pump unit at the flanges thereof. A stationary cylinder is then integrated in the interior of that module, with a piston being movably provided therein, wherein the piston can be suitably fixedly connected to the shaft of the pump impeller wheel or the drive unit.

In another design configuration the retrofit module can be fixed directly on the shaft of the pump impeller wheel or the drive unit, in the form of a set or a structural unit consisting of piston and cylinder, in an existing structural space or a structural space which is to be provided between the drive unit and the pump unit. The cylinder can for example be fixed to the housing of the drive unit so that the piston is held displaceably therein.

In that way it is possible for the axial thrust compensating arrangement according to the invention to be retrofitted in conventional vertical pumps at a low level of complication and expenditure, in order in that way further to increase the operational reliability and service life thereof.

In this connection it should also be mentioned that the above-described feed for the predetermined low pressure by way of a compensating conduit which is in the form of an axial passage in a shaft in the vertical pump is particularly suitable for retrofitting existing pumps with the axial thrust compensating arrangement proposed herein. Retrofitting such a pressure conduit or compensating conduit substantially involves replacing the shaft, with structural interventions in the pump housing being very substantially eliminated. The axial passage required in the shaft can be particularly easily embodied in vertical pumps of a modular structure in which the use-related pump dimensioning is effected by way of the number of installed rotary pump modules or drive modules respectively, that is to say scaling. In that respect the required axial shaft passages can be technically easily produced in the form of bores, by virtue of the relatively short length dimension thereof.

In regard to the method of compensating for the axial thrust in a pump, in particular a vertical pump, it is to be noted that this method affords the same advantages as the above-mentioned advantages of the described arrangement. In that respect the method of compensating for an axial thrust acting on a shaft of a pump, in particular a vertical pump comprising at least one rotary pump unit and at least one drive unit for the rotary pump unit, in operation of the pump, comprises: producing a differential pressure from the pump pressure produced in operation and a lower pressure than the pump pressure, wherein the lower pressure or the pump pressure is fed to the compensating piston by way of an axial bore in the shaft as a compensating conduit; and producing from the differential pressure a force which acts in opposite relationship to the axial thrust at the shaft and which at the shaft self-regulatingly reduces the axial thrust occurring in operation of the pump by means of the differential pressure.

The method of retrofitting an arrangement for the compensation of the axial thrust makes it possible to equip conventional pumps with the arrangement according to the invention so that those pumps can also enjoy the above-mentioned advantages. The method of retrofitting axial thrust compensation on a pump comprising at least one rotary pump unit and at least one drive unit for the rotary pump has for that purpose: mounting a piston to the pump shaft; mounting to the pump a cylinder for guiding the piston; producing a feed for the pump pressure produced in operation to the side of the piston which faces in the direction of the axial thrust; producing a feed for a predetermined lower pressure than the pump pressure to the other side of the piston, wherein one of the feeds is an axial passage in the shaft; and setting up the assembly of the piston and the cylinder so that in operation of the pump a pressure difference can thus be self-regulatingly produced, wherein a force which is dependent on the axial thrust of the pump and which is in opposite relationship thereto acts on the shaft by means of the pressure difference at the pump shaft.

The retrofitting method can also comprise: adapting the assembly of the compensating cylinder and the compensating piston to the output of the drive unit of the pump so that a reversal of the axial thrust can be excluded at any time.

Finally the retrofitting method can further comprise: equipping a part or the entire shaft of the pump with an axial passage in the part of the shaft extending through the drive unit and/or in the part of the shaft extending through the rotary pump unit, wherein the passage is adapted to feed the pump pressure produced in operation or a predetermined lower pressure than the pump pressure to a side of the piston.

For the aforementioned retrofitting method it is possible to provide a corresponding retrofit module for retrofitting the axial thrust compensation means proposed herein to existing pumps, with which the same advantages and effects as described hereinbefore can be achieved. The retrofit model is accordingly suitable for a pump comprising at least one rotary pump unit with at least one impeller wheel driven by at least one drive unit, wherein an axial thrust corresponding to the pump pressure acts on a shaft of the impeller wheel in operation of the pump. The retrofit module is designed for self-regulating production of a compensating force which at least partially relieves the load of the axial thrust, by means of a pressure difference from the pump pressure and a predetermined lower pressure with an arrangement comprising a compensating piston and a compensating cylinder. For that purpose the compensating piston of the retrofit module can be connected force-lockingly to the shaft of the rotary pump unit in the axial direction and in that case guided in the compensating cylinder of the retrofit module, which can be stationarily fixed to the pump.

DRAWINGS

Embodiments by way of example of the invention are described hereinafter with reference to the accompanying drawings. The terms ‘top’, ‘bottom’, ‘left’ and ‘right’ used in the description of the specific embodiment relate to the drawings in an orientation with the references and the Figure legends normally readable, in which:

FIG. 1 shows a longitudinal section through a pump according to the invention,

FIG. 2 shows a compensating piston/cylinder assembly according to the invention, and

FIG. 3 shows a further configuration of the arrangement according to the invention.

DETAILED DESCRIPTION

FIG. 1 shows an embodiment by way of example of a vertical pump. In this connection, in the simplest case the term vertical pump is used to denote the combination of a drive unit with a rotary pump unit, which are arranged one above the other substantially perpendicularly to the level on which the pump stands. As noted in the opening part of this specification, the term vertical pump is used here to denote a pump in which in use the pump shaft is oriented substantially vertically. Furthermore it should be established for clarification purposes that, for a vertical pump, when pumping a fluid against the force of gravity ‘down’ is defined in relation to the vertical pump by the suction side of the pump unit and correspondingly ‘up’ in relation to the vertical pump corresponds to the pressure side of the pump unit.

The vertical pump shown in FIG. 1 comprises a drive unit 1 which can be for example an electric motor and a rotary pump unit 2 which is fixed to the drive unit 1 by means of a flange connection. A drive shaft or a shaft 4 of the drive unit 1 is oriented perpendicularly. It projects with its lower end out of the housing of the drive unit 1. An impeller wheel 5 of the rotary pump unit 2 is fixed on that end of the shaft 4 and is secured in positively locking relationship to prevent rotation thereof on the shaft for example by means of a slot/key connection 6 and is secured at the end of the shaft by a nut 7 to prevent it from slipping off or dropping down. Arranged around the impeller wheel 5 is a pump housing 8 which is flange-connected with its upper end to the drive unit 1 by means of a flange connection 3. The lower end forms the suction intake opening 9 of the pump 2.

Disposed between the drive unit 1 and the rotary pump unit 2 is a piston/cylinder assembly according to the invention for axial thrust compensation. It comprises a compensating piston 10 which is fixed on the shaft 4 non-rotatably and axially non-displaceably, and a cylinder 14. Both preferably comprise corrosion-resistant steel, for example Niro steel, Duplex, NiResist or cast bronze.

The cylinder 14 is fixedly connected to the underside of the drive unit 1 and oriented coaxially with the shaft 4 of the drive unit 1. It separates off the top side and the underside 11, 12 of the piston 10 from each other in substantially fluid-tight relationship but not necessarily in fluid-tight relationship. It has been found that a gap dimension is adequate in the sense of fluid-tight, at which the influence of frictional forces in the piston-cylinder assembly according to the invention is reduced. Thus, a load-relief chamber 15 is disposed in the cylinder 14 between the top side 11 of the piston and the housing of the drive unit 1. In the non-loaded condition, corresponding to FIG. 1, the piston 10 is in the cylinder 14 but spaced in relation to the underside of the housing of the drive unit 1. The underside 12 of the piston 10 is in direct fluidic communication with the high-pressure side of the rotary pump unit 2. Above the flange connection 3 compensating conduits 18 are passed from the outside horizontally through the housing of the drive unit 1 and communicate with the load-relief chamber 15. A selected or predetermined low pressure which can be for example the suction pressure or the ambient pressure is fed by way of those compensating conduits 18 through further passages (not shown) or conduits of a different configuration, to the top side 11 of the piston. It is noted that the term ‘lower pressure’ is used here to denote any predetermined pressure which is lower than the pump pressure currently occurring in operation of the pump.

The compensating conduits 18 for feeding a selected or predetermined lower pressure can be avoided if, as mentioned above, an axial passage (not shown in the Figures), for example in the form of a bore, is provided through the shaft 4 of the drive unit 1 and communicates with the load-relief chamber 15. In that case the axial bore, as shown in FIG. 1, can be passed from above into the region of the compensating piston 10 when the ambient pressure is to be supplied as the predetermined low pressure. In a corresponding fashion the axial bore in the shaft 4 is passed from below into the region of the compensating piston 10 if the suction pressure is to be supplied as the predetermined low pressure.

FIG. 2 diagrammatically shows another embodiment of the assembly of the piston and the cylinder (piston/cylinder assembly) for axial thrust compensation. The operating principle however is basically the same as in the assembly of FIG. 1. The compensating piston 10 is again arranged on the shaft 4. It is guided in the cylinder 14 which separates the underside 12 of the piston from the top side 11 in substantially fluid-tight relationship, for example as described above by a small gap. The load-relief chamber 15 enclosed by the cylinder 14 and the piston 10 is connected to the high-pressure side of the rotary pump unit 2, thus acting on the underside 12 of the piston. The top side 11 is subjected to the action of a lower pressure. The assembly in FIG. 2 additionally forms a hydrostatic additional bearing, the advantages of which are described in greater detail hereinafter.

FIG. 3 shows a further embodiment of the arrangement according to the invention. The piston/cylinder assembly according to the invention is here arranged above the vertical pump, above the housing of the drive unit 1. The shaft 4 of the drive unit 1 is prolonged to such an extent that it projects above the upper end of the drive unit. The compensating piston 10 is fixed at that end. It is enclosed laterally and additionally also upwardly and downwardly by the cylinder 14. That means that chambers 15, 16 are formed on both sides of the piston 10. The cylinder is fixed to the housing of the drive unit 1 so that the piston 10 is guided slidably perpendicularly therein. The chamber 15 above the piston 10 communicates with the ambient atmosphere by way of a compensating conduit, that is to say ambient pressure obtains in the chamber 15, the chamber 16 therebeneath is supplied with the pump pressure. As a result, in operation a pressure difference is formed at the piston 10, which lifts the shaft 4 against the axial thrust involved. It is to be appreciated that this design configuration is used in the situation where the drive shaft 4 is at the same time also the shaft of the impeller wheel or both shafts are axially fixedly connected together or the shaft is of an integral structure.

In the embodiment of FIG. 3, as an advantageous development—as already referred to hereinbefore in connection with the feed of a predetermined lower pressure than the pump pressure—it is possible for the pump pressure to be fed to the chamber 16 from above by means of an axial bore in the shaft 4 of the drive unit 1.

In operation of the vertical pump in FIG. 1 a fluid to be delivered, for example ground water or pit water, is conveyed through the suction intake opening 9 substantially in an axial direction upwardly, that is to say in the delivery direction, by the rotary pump unit 2, in which it is guided past the drive unit by means of suitable passages 20 in the housing of the drive unit. The axial thrust which is produced by the delivery thrust and which is in opposite relationship thereto acts on the impeller wheel and by way thereof urges the pump shaft 4 downwardly in opposite relationship to the delivery direction of the pump 2.

As the impeller wheel 5 of the rotary pump unit 2 in accordance with the design structure in FIG. 1 is fixed directly on the shaft 4 of the drive unit 1, the axial thrust also acts directly on the shaft 4 of the drive unit 1, whereby the axial bearing of the drive unit 1 is subjected to an additional loading corresponding to the axial thrust.

The pump pressure occurring due to operation of the rotary pump unit 2 however also acts directly on the underside 12 of the compensating piston 10. A defined lower pressure is applied at the top side 11 of the piston 10. As a result, a differential pressure occurs in the assembly consisting of the compensating piston 10 and the cylinder 14, as the pressure difference deriving from the pump pressure and a defined lower pressure. A force acting on the compensating piston 10 is produced from the differential pressure, over the predetermined piston area. As the pressure on the underside 12 of the piston 10 is greater than on the top side 11 thereof, that compensating force which is produced from the differential pressure is directed upwardly (in the direction of the drive unit or in the delivery direction). The compensating force acts in opposition to the axial thrust and causes the piston 10 to be moved upwardly in the cylinder 14. As the cylinder 14 is fixed to the shaft 4 the compensating force correspondingly acts on the shaft 4 and thus relieves the load on the thrust bearing of the drive unit 1.

The load-relief force which is produced by the pressure difference with a constant piston area at the piston 10 depends on the pump pressure and the selected lower pressure. With an increasing pump pressure and a constant or decreasing suction pressure, the load-relief force which acts in opposition to the axial thrust increases. As the axial thrust also increases with an increasing delivery pressure, that provides for self-regulating adaptation of the axial thrust load-relief effect to the axial thrust. The axial thrust falls with a decreasing delivery pressure. The falling delivery pressure however means that the pressure difference also falls at the compensating piston 10, whereby the load-relief force produced also falls. With a decreasing delivery pressure therefore adaptation of the load-relief force to the axial thrust also takes place in a self-regulating fashion.

At the maximum pump output, that is to say at the maximum delivery pressure, both the greatest axial thrust and also the greatest load-relief force at the compensating piston 10 occurs. As the load-relief force is proportional to the piston area, when the pressure difference is constant, the piston area can be so designed that, in the range of the maximum axial thrust, there is a desired reduction in the force acting on the thrust bearing in such a way that the thrust bearing is always running in the range for which it was specified. In addition that avoids a reversal of force by the load-relief force, which would additionally load the axial thrust bearing which is normally designed to be much weaker.

An embodiment of the piston/cylinder assembly for axial thrust compensation as shown in FIG. 2 forms an additional hydrostatic bearing as already mentioned above. Delivery pressure obtains in the load-relief chamber 15. The axial thrust acts in opposition thereto by way of the shaft 4 and the compensating piston 10. As described hereinbefore during operation of the rotary pump unit an equilibrium occurs in self-regulating fashion between the axial thrust and the load-relief force in accordance with the pressure difference obtaining at the compensating piston 10 and the size of the piston area. That assembly thus forms a hydraulic bearing. In other words, the compensating piston is not supported against a second running surface but on a fluid cushion formed by the delivery pressure in the cylinder 14. The bearing thus runs in an approximately wear-free manner and has a markedly lower frictional resistance. If, as described hereinbefore, the assembly of the compensating piston 10 and the compensating cylinder 14 must be arranged upstream of the rotary pump unit 2 in the delivery direction, the compensating cylinder 14 must be fixedly connected to the pump housing 8 so that the compensating piston 10 can be guided slidably therein. Passing the shaft 4 through the bottom of the cylinder 14, as shown in FIG. 2, is not necessary in this construction. The pump pressure must be fed to the load-relief chamber 15 by way of a compensating conduit (not shown in greater detail).

It is to be noted that the invention is not limited to the embodiments by way of example described herein with reference to FIGS. 1 through 3. If the pump and the drive unit have separate shafts, it will be appreciated that it is possible for the compensating piston/cylinder assembly to be disposed only in the pump or only in the drive unit. It is also conceivable for the arrangement according to the invention to be implemented with two pistons, in which case the pistons are respectively subjected on one side to the higher and the lower pressure respectively and the corresponding other sides of the pistons communicate with each other, in which case the pressure difference can be additionally influenced or adjusted, with different piston areas.

To sum up it is to be noted that here there has been proposed compensation for the axial thrust involved in a pump, in particular a vertical pump, having at least one drive unit and at least one rotary pump unit. In an embodiment in operation of the pump a compensating piston which is axially non-displaceably connected to the shaft of the impeller wheel of the rotary pump unit is subjected to the action of a pressure difference which results from the pump pressure and a lower pressure and from which there is produced a force which is directed in opposite relationship to the axial thrust and which acts on the shaft of the impeller wheel. There is also proposed a method of axial thrust compensation and a method of retrofitting an arrangement for axial thrust compensation to a pump, in particular a vertical pump, as well as a corresponding retrofit module therefore in existing pumps. 

1. A pump comprising: at least one rotary pump unit with at least one impeller wheel driven by at least one drive unit, wherein an axial thrust corresponding to the pump pressure acts on a shaft of the at least one impeller wheel in operation of the pump, wherein the pump has a compensating piston for self-regulating production of a compensating force that at least partially relieves the load of the axial thrust by means of a pressure difference from the pump pressure and a predetermined lower pressure, wherein the compensating piston is connected to the shaft in force-locking relationship in the axial direction of the shaft and is guided movably in a stationary compensating cylinder, and wherein the communication of the pump pressure or the predetermined lower pressure to the compensating piston comprises an axial passage in the shaft.
 2. A pump as set forth in claim 1 wherein the effective piston area is matched to the nominal output of the drive unit.
 3. A pump as set forth in claim 1 wherein the pump is a vertical pump.
 4. A pump as set forth in claim 1 wherein the assembly comprising the compensating piston and the compensating cylinder is between the drive unit and the rotary pump unit.
 5. A pump as set forth in claim 1 wherein the compensating cylinder is fixed at the side of the drive unit, that faces in the direction of the pump.
 6. A pump as set forth in claim 1 wherein the pump pressure of the rotary pump unit is fed by means of a direct fluidic communication to the side of the rotary pump unit, that is towards the compensating piston.
 7. A pump as set forth in claim 1 wherein in operation of the pump the predetermined lower pressure is fed by way of a compensating conduit to the side of the rotary pump unit, that is remote from the compensating piston.
 8. A pump as set forth in claim 1 wherein the assembly comprising the compensating piston and the compensating cylinder is fixed upstream of the rotary pump unit in the delivery direction.
 9. A pump as set forth in claim 8 wherein the assembly comprising the compensating piston and the compensating cylinder additionally is a hydraulic bearing.
 10. A pump as set forth in claim 8 wherein the pump pressure of the rotary pump unit is fed by way of a compensating conduit to the side of the rotary pump unit, that is remote from the compensating piston.
 11. A pump as set forth in claim 1 wherein the predetermined lower pressure is the suction pressure of the pump, that is produced in operation of the pump, or wherein the predetermined lower pressure is the ambient pressure prevailing at the location of operation.
 12. A pump as set forth in claim 1 wherein the axial passage is in the part of the shaft that extends in the rotary pump.
 13. A pump as set forth in claim 1 wherein the axial passage is in the part of the shaft that extends in the drive unit.
 14. A pump as set forth in claim 1 wherein the assembly comprising the compensating piston and the compensating cylinder is in the form of a module arranged between the pump and the drive unit.
 15. A pump as set forth in claim 14 wherein the module is a retrofit module for retrofitting to an existing pump.
 16. A method of compensating an axial thrust acting on a shaft of a pump, comprising at least one rotary pump unit and at least one drive unit for the rotary pump unit, in operation of the pump, comprising the steps: producing a differential pressure between the pump pressure that is produced in operation and a lower pressure than the pump pressure, wherein communicating the lower pressure or the pump pressure to the compensating piston by an axial bore in the shaft, and producing from the differential pressure a force that acts in opposite relationship to the axial thrust at the shaft and at the shaft self-regulatingly reducing the axial thrust occurring in operation of the pump by means of the differential pressure.
 17. A method of retrofitting axial thrust compensation to a pump comprising at least one rotary pump unit and at least one drive unit for the rotary pump, wherein the method comprises: mounting a piston to the pump shaft, mounting to the pump a cylinder in which the piston can be guided, producing a feed for the pump pressure produced in operation to the side of the piston, that faces in the direction of the axial thrust, producing a feed for a predetermined lower pressure than the pump pressure to the other side of the piston, wherein one of the feeds is an axial passage in the shaft, and setting up the assembly of the piston and the cylinder so that in operation of the pump a pressure difference can be self-regulatingly produced therewith, wherein a force which is dependent on the axial thrust of the pump and in opposite relationship thereto acts on the shaft by means of the pressure difference at the pump shaft.
 18. A method as set forth in claim 17 and further comprising: matching the assembly of the compensating cylinder and the compensating piston to the output of the drive unit of the pump.
 19. A method as set forth in claim 17 and further comprising: equipping a part or the entire shaft of the pump with an axial passage in the part of the shaft that extends through the drive unit and/or in the part of the shaft that extends through the rotary pump unit, wherein the passage is capable of communicating the pump pressure produced in operation or a predetermined lower pressure than the pump pressure to a side of the piston.
 20. A retrofit module for a pump comprising at least one rotary pump unit having at least one impeller wheel driven by at least one drive unit, wherein in operation of the pump an axial thrust corresponding to the pump pressure acts on a shaft of the impeller wheel, the retrofit module comprises: an assembly comprising a compensating piston and a compensating cylinder capable of self-regulatingly producing a compensating force which at least partially relieves the load of the axial thrust by means of a pressure difference from the pump pressure and a predetermined lower pressure, wherein the compensating piston of the retrofit module is capable of being connected to the shaft of the rotary pump unit in force-locking relationship in the axial direction and in that case is guided movably in the compensating cylinder of the retrofit module, which compensating cylinder can be stationarily fixed to the pump. 